Capital gains tax is more difficult to avoid than many investors may think.

Take retired maths teachers Fergus and Judith Wilson (pictured below), who shot to fame by amassing, over a period of about 15 years, a vast portfolio of properties to let in Ashford, Kent. Their 1,000-strong buy-to-let portfolio of two-bedroom and three-bedroom houses is worth £200m or more. When they announced this week that it was all up for sale, one of my first questions to 66-year-old Fergus was: “What is your capital gains tax liability?”

While forthright in his opinions on government housing policy, immigration and much else, Mr Wilson is reticent on personal financial details, but he did say: “I live in Britain and I’ll pay every bean of tax due. You can reduce the gain a little with purchase and disposal costs but it will be a big tax bill.

"The Government will be happy.”

My rough estimate is that after the Wilsons have cleared their buy-to-let mortgages and accounted for other allowable reductions to their gains, they will owe £30m in tax.

The Wilsons’ case is off the scale, of course, but it highlights a problem that millions of smaller investors face. Capital gains tax is not as avoidable as people appear to believe.

In Thursday’s Telegraph, novelist and financial commentator Matthew Lynn pointed out that, since the Government raised the capital gains tax rate in 2010 from 18pc to 28pc, the amount of tax collected had fallen.

His argument was that – as has been demonstrated many times with other taxes here and abroad – the higher the tax rate, the more avoidance is encouraged, with the upshot that less is collected. “Without breaking any laws, it [capital gains tax] is largely a voluntary tax,” he said.

While recent years’ tax take figures support Mr Lynn’s view (see table, below), a different reality is emerging, and it’s shown in the italicised forecast tax take figures produced by the Office for Budget Responsibility. Like it or not, the capital gains tax regime is closing in. Those who own assets which have risen substantially in value are cornered. With few exceptions, if owners sell, or even give the assets to their children or anyone else, they crystallise the gain and pay the tax. If they don’t sell during their lifetime the asset is swept into their estate where – an outcome possibly far worse than the capital gains tax bill – it will become liable to inheritance tax.

That’s how the pincer operates. It’s a case of heads the taxman wins, tails you lose.

Capital gains tax on property you’ve lived in

This is where the big tax let-offs have historically been found, and they are useful for “accidental landlords” – those who own one or two properties in addition to their home, perhaps because they previously traded up without selling.

If a property has ever been your main residence, it qualifies for two reliefs: “principal private residence relief” and “private letting relief”. Depending on how long you lived there, and how long you let it for, the gains on the property can be effectively whittled down or eliminated – as so many London flat-flipping MPs have discovered to their profit in recent years.

But the Government is closing these loopholes down by reducing the time period during which gains are tax-exempt, and also making it harder to choose which of your properties you nominate as your main residence.

Capital gains tax on property you’ve never lived in

Here, property owners are caught in the headlights. Costs associated with buying, selling and improving the property are allowable to offset gains, and there is the owner’s annual capital gains tax allowance, but long-term owners will find that these go no distance in cutting a bill. There’s nowhere to hide.

Capital gains tax on shares and funds

Readers’ letters and emails suggest that capital gains tax on shares, and difficulties calculating the liability, are a growing concern. There are several reasons for this, one being the removal in 2008 of “taper relief”, which until then had reduced taxable gains according to the length of time an asset was owned. The effects of this change are now filtering through – with an arguably unfair impact on long-term shareholders.

A speculative shareholding whose value quadrupled in a month attracts the same tax as a chugging blue chip that delivered modest, above-inflation growth over a decade.

In the coming weeks and months we'll look in detail at several aspects of capital gains tax and how to reduce potential liabilities, so please keep reading. And please email any particular suggestions, questions or observations about this troublesome tax to money@telegraph.co.uk.